Conventionally, most of scrapped home appliances are shredded, valuables such as metals are recovered, and the remainders are disposed of as industrial wastes to a “least controlled landfill site” where the wastes are merely buried in a dug hole.
In recent years, a shortage of the capacity of disposal sites poses a serious problem, and environmental pollution by hazardous substances also poses a serious problem. For example, the cathode ray tube of a television uses a large amount of lead-containing glass. According to trial calculation by the Environment Agency, lead contained in scrapped cathode ray tubes amounts to 20,000 t every year, and most of lead is buried in least controlled landfill sites. However, rainwater naturally permeates in least controlled landfill sites, and these sites are not equipped with any drainage facility. It is being recognized that lead as a hazardous substance may diffuse.
Under these circumstances, conventional processing methods must be reconsidered. As for the cathode ray tube of a television, studies of shredding cathode ray tube glass into cullets (small glass pieces) and reusing them for cathode ray tubes have been made by Association for Electric Home Appliances. Of these studies, a system of extracting a cathode ray tube from a television main body and shredding the cathode ray tube into glass cullets has been developed (see, e.g., “Electrotechnology”, January, 1997).
A method of recovering glass as cullets is disclosed in, e.g., Japanese Laid-Open Patent Application No. 61-50688. There is also known a method of shredding cathode ray tube glass into cullets (small glass pieces) and reusing them for cathode ray tubes (e.g., Japanese Laid-Open Patent Application No. 9-193762). A method of separating a cathode ray tube into a face plate and funnel in accordance with materials, and shredding them into cullets is disclosed in, e.g., Japanese Laid-Open Patent Application No. 05-185064. Further, a method of separating a cathode ray tube into a face plate and funnel, peeling fluorescent substances and a black mask from the face plate, and recycling the face place is disclosed in Japanese Laid-Open Patent Application No. 7-037509.
To reuse cathode ray tube glass, the glass must be separated into panel glass and lead-containing funnel glass. This is because, if lead is mixed in panel glass by a predetermined amount or more, a browning phenomenon occurs, and the lead-containing glass cannot be reused as a raw material of the panel glass. For this reason, a cathode ray tube is separated into a panel and funnel. For this purpose, there are proposed a method of defining a position to cut a cathode ray tube (Japanese Laid-Open Patent Application No. 9-115449), and a method of melting frit glass which joins a panel and funnel, thereby separating the panel and funnel (Japanese Laid-Open Patent Application No. 7-45198).
As a technique of separating a funnel and panel welded with frit glass, a technique of separating a funnel and panel using thermal distortion in heat treatment is known as disclosed in, e.g., Japanese Laid-Open Patent Application Nos. 5-151898, 7-029496, 9-200654, and 9-200657.
In recent years, studies for applying cold cathode elements have enthusiastically been done. Known examples of the cold cathode elements are surface-conduction type electron-emitting elements, field emission type electron-emitting elements, metal/insulator/metal type electron-emitting elements. Compared to a thermionic cathode element, the cold cathode element can emit electrons at a low temperature. The cold cathode element does not require any heater, is simpler in structure than the thermionic cathode element, and can form a small element. Even if many elements are arranged on a substrate at a high density, problems such as thermal melting of the substrate hardly arise. In addition, the response speed of the thermionic cathode element is low because it operates upon heating by a heater, whereas the response speed of the cold cathode element is high.
Of cold cathode elements, surface-conduction type electron-emitting elements have a simple structure, can be easily manufactured, and allow forming many elements in a wide area. As disclosed in Japanese Laid-Open Patent Application No. 64-31332 filed by the present applicant, a method of arranging and driving many elements has been studied.
As applications of surface-conduction type electron-emitting elements, e.g., image forming apparatuses such as an image display apparatus and image recording apparatus, charge beam sources, and the like have been studied.
Particularly as applications to image display apparatuses, as disclosed in U.S. Pat. No. 5,066,883 and Japanese Laid-Open Patent Application Nos. 2-257551 and 4-28137, an image display apparatus using a combination of a surface-conduction type electron-emitting element and a fluorescent substance which is irradiated with an electron beam to emit light has been studied. The image display apparatus using a combination of a surface-conduction type electron-emitting element and fluorescent substance is expected to exhibit more excellent characteristics than other conventional types of image display apparatuses. For example, this image display apparatus is superior to a recent popular liquid crystal display apparatus in that the image display apparatus does not require any backlight because of self-emission type and that the view angle is wide.
A method of driving many field emission type electron-emitting elements arranged side by side is disclosed in, e.g., U.S. Pat. No. 4,904,895. A known application of FE type electron-emitting elements to an image display apparatus is a flat display reported by R. Meyer et al. [R. Meyer: Recent Development on Micro-tips Display at LETI”, Tech. Digest of 4th Int. Vacuum Micro-electronics Conf., Nagahama, pp. 6-9 (1991)].
An application of many metal/insulator/metal type electron-emitting elements arranged side by side to an image display apparatus is disclosed in Japanese Laid-Open Patent Application No. 3-55738.
Of these image forming apparatuses using electron-emitting elements, a thin flat display is space-saving and lightweight, and receives a great deal of attention as a substitute for a cathode ray tube type image display apparatus.
The interior of the airtight container in the image forming apparatus is kept at a vacuum of about 10−6 Torr. As the display area of the image display apparatus increases, the airtight container requires a means for preventing a rear plate and face plate from being deformed or destructed by the difference between internal and external pressures of the airtight container. If the rear plate and face plate are made thick, this increases the weight of the image display apparatus, and generates distortion and disparity of an image when viewed diagonally. Thus, the airtight container generally employs spacers each of which is made of a relatively thin glass plate whose surface is covered with an antistatic conductive film.
Flat displays including a vacuum fluorescent display (VFD), plasma display (PDP), and surface-conduction type electron source display (SED) in addition to the field-emission type electron source display (FED) and MIM type display described above are space-saving and lightweight, and receive a great deal of attention as substitutes for cathode ray tube type display apparatuses. Many flat displays have been studied and developed.
For example, the present applicant offers several proposals for an electron source constituted by arraying on a substrate many surface-conduction type electron-emitting elements as one type of cold cathode type electron-emitting elements, and an image display apparatus using this electron source.
The structure of the surface-conduction type electron-emitting element, the structure of the image display apparatus using this, and the like are disclosed in detail in, e.g., Japanese Laid-Open Patent Application No. 7-235255, and will be described briefly.
FIGS. 68A and 68B show a structure of a surface-conduction type electron-emitting element. Reference numeral 411 denotes a substrate; 412 and 413, a pair of element electrodes; and 414, a conductive film which partially has an electron-emitting portion 415. The substrate 411, element electrodes 412 and 413, conductive film 414, and electron-emitting portion 415 constitute an electron-emitting element 416.
As a method of forming the electron-emitting portion 415, a voltage is applied between the pair of element electrodes 412 and 413 to deform, change of properties, or destruct part of the conductive film, thereby increasing the resistance. This is called “electrification forming processing”. To form an electron-emitting portion having good electron emission characteristics by this method, the conductive film is preferably made of fine conductive particles. An example of the material is fine PdO particles. The voltage applied in electrification forming processing is preferably a pulse voltage. This processing can adopt either one of a method of applying pulses having a predetermined peak value, as shown in FIG. 69A, and a method of applying pulses whose peak value gradually increases, as shown in FIG. 69B.
To form a fine conductive particle film, fine conductive particles may be directly deposited by gas deposition. Instead, a method of applying the solution of a compound (e.g., organic metal compound) containing the constituent element of the conductive film and annealing the coating into a desired conductive film is desirable because no vacuum device is required, the manufacturing cost is low, and a large electron source can be formed. As a method of applying the organic metal compound solution, a method of applying the solution to only a necessary portion using an ink-jet apparatus is desirable because the method does not require any extra step for patterning of the conductive film.
After the electron-emitting portion is formed, a pulse voltage is applied between the element electrodes in a proper atmosphere containing an organic substance (this will be called “activation processing”). Then, a deposition film mainly containing carbon is formed at the electron-emitting portion and its vicinity to increase a current flowing through the element and improve electron emission characteristics.
After that, a step called “stabilization processing” is preferably performed. In this processing, while a vacuum container and electron-emitting element are heated, the vacuum container is kept evacuated to sufficiently remove an organic substance and the like, thereby stabilizing the characteristics of the electron-emitting element.
A method of forming the conductive film of an electron source using a surface-conduction type electron-emitting element by an ink-jet apparatus is disclosed in, e.g., Japanese Laid-Open Patent Application No. 8-273529.
The ink-jet apparatus will be explained briefly. Methods of discharging ink from the ink-jet apparatus are roughly classified into two types. According to the first method, a liquid is discharged as droplets using the contraction pressure of a piezoelectric element disposed at a nozzle. This method is called a piezo-jet method. In this method, a conductive thin film material is stored in an ink reservoir, and a predetermined voltage is applied to an electrical signal input terminal to contract the cylindrical piezoelectric element, thereby discharging a liquid as droplets.
According to the second method, a liquid is heated and bubbled by a heating resistor to discharge droplets. This method is called a bubble-jet method. In a bubble-jet type ink-jet apparatus, the heating resistor generates heat to bubble a liquid, thereby discharging droplets from a nozzle.
By using this ink-jet apparatus, an organic metal compound solution is applied as droplets to only a predetermined position. After the solution is dried, the organic metal compound is thermally decomposed by heating processing to form a conductive film from small particles of a metal or metal oxide.
FIG. 1 shows a structure of an image display apparatus. In FIG. 1, reference numeral 1 denotes a rear plate; 2, a face plate having a fluorescent film 2b, metal back 2c, and the like formed on the inner surface of a substrate 2a; and 3, a support frame. The rear plate 1, support frame 3, and face plate 2 are joined and tightly sealed with frit glass to constitute an image display apparatus 15.
Flat panel displays having this structure are expected to abruptly increase in size and production. In these flat panel displays, frit glass used for sealing contains lead. The fluorescent substance 2b serving as an image forming member, a spacer 4, and the like are high-cost members. Similar to cathode ray tube glass, establishment of a recovery system becomes an important subject in terms of “non-hazardous processing”, “volume reduction”, and “recycling”.